Method and apparatus for providing uninterrupted power during transitions between a power source and a standby generator using capacitor supplied voltage

ABSTRACT

A method and apparatus for providing uninterrupted power during transitions between a primary power source and a standby power generator. The method and apparatus includes determining one of a power failure condition and a power return condition of the primary power source, transitioning between the primary power source and the standby power generator, and providing power to a load during the transition, the power being supplied by an uninterruptable power supply (UPS) having a capacitor supplied voltage.

TECHNICAL FIELD

[0001] This invention relates generally to a method and apparatus forproviding uninterrupted power to a load during transitions between aprimary power source and a standby power generator and, moreparticularly, to a method and apparatus for providing uninterruptedpower using a capacitor supplied voltage.

BACKGROUND ART

[0002] It has long been a common practice to start standby powergenerators using the energy stored in batteries to drive starter motors,which in turn crank the generator until the generator starts. However,the load placed upon the batteries reduces the life of service of thebatteries significantly. A typical battery for starting a standby powergenerator may only have a useful life of about three years. In addition,the power output of even a good battery may be severely reduced whenused under extreme temperature conditions.

[0003] Advances have been made in technology regarding capacitors, whichare capable of storing electrical energy, but until recently were notcapable of storing the amounts of energy needed to start a generator.However, large capacitance capacitors, for example electric double layercapacitors, have been developed which are capable of storing largeamounts of electrical energy. These capacitors are sometimes known assuper capacitors, and are finding use in applications such as in enginestarting circuits.

[0004] Although the transition between a primary power source and astandby power generator may be accomplished very quickly, the briefinterruption in power may have an adverse effect on some types of loads;for example, sensitive electronic equipment, digital clocks, timers, andthe like. For this reason, uninterruptable power supplies (UPS) arecommonly used to prevent power interruptions of any duration.

[0005] Typically, a UPS uses batteries to provide the electric powerneeded during the transition periods between primary power sources andgenerators. However, as described above, batteries have limited usefullives (about three years) due to the loads placed upon them. Inaddition, batteries do not function as well under extreme climateconditions. In a situation where a UPS must supply a large amount ofpower, the batteries needed may require a dedicated room or building tohouse them. In extreme climate conditions, e.g., extreme cold climates,the dedicated housings for the batteries would need to be climatecontrolled, thus requiring additional complex and costly equipment.

[0006] The present invention is directed to overcoming one or more ofthe problems as set forth above.

DISCLOSURE OF THE INVENTION

[0007] In one aspect of the present invention a method for providinguninterrupted power during transitions between a primary power sourceand a standby power generator is disclosed. The method includes thesteps of determining one of a power failure condition and a power returncondition of the primary power source, transitioning between the primarypower source and the standby power generator, and providing power to aload during the transition, the power being supplied by anuninterruptable power supply (UPS) having a capacitor supplied voltage.

[0008] In another aspect of the present invention an apparatus forproviding uninterrupted power during transitions between a primary powersource and a standby power generator is disclosed. The apparatusincludes a transfer switch adapted to determine one of a power failurecondition and a power return condition of the primary power source, andresponsively transition between the primary power source and the standbypower generator, an uninterruptable power supply (UPS) for providingpower to a load during the transition, and at least one capacitorelectrically connected to the UPS for providing the power to the load.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is an electrical block diagram illustrating a preferredembodiment of the present invention;

[0010]FIG. 2 is a power vs. time graph illustrating charging anddischarging times of a capacitor used in the circuit of FIG. 1;

[0011]FIG. 3 is a current vs. time graph illustrating current deliveryvs. time of a capacitor and a battery; and

[0012]FIG. 4 is a flow diagram illustrating a preferred method of thepresent invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0013] Referring to the drawings, and with particular respect to FIG. 1,a diagrammatic illustration of a preferred embodiment of the presentinvention is shown. It is noted that the embodiment shown in FIG. 1 isillustrative of but one aspect of a preferred apparatus 100 suitable foruse with the present invention. Variations of the apparatus 100 may beemployed which are suitable for use with the invention as describedbelow with respect to the specification and the accompanying claims.

[0014] A primary power source 102 provides primary electrical power to aload 106. The primary power source may be of any type well known in theart, such as electrical power provided by an electrical power utilitycompany, or an electrical power generating station of some type.

[0015] A standby power generator 104 having a capacity suitable forproviding standby electrical power to the load 106 is available toprovide standby power during periods of time of power failure of theprimary power source 102. Typically, the standby power generator 106 isdriven by an internal combustion engine (not shown), as is well known inthe art.

[0016] A transfer switch 128, electrically connected between the primarypower source 102, the standby power generator 104, and the load 106, isadapted to determine a power failure condition of the primary powersource 102, disconnect the primary power source 102 from the load 106,and connect the standby power generator to the load 106. In addition,the transfer switch 128 is adapted to enable a starter system enableswitch 130, which in turn is adapted to enable a starter system 108.

[0017] Preferably, the starter system 108 is of a type typically used tostart internal combustion engines, and is therefore well known in theart.

[0018] A starter system activate switch 132 is adapted to sense the lossof electrical power from the primary power source 102 via electricalpath A-B-C, and responsively activate the starter system 108 byconnecting a first capacitor 118 to the starter system 108. In thepreferred embodiment, the first capacitor 118 is of a type commonlyknown as a super capacitor, e.g., an electric double layer capacitor,and is capable of storing electrical energy sufficient to provide avoltage to drive the starter system 108 to start the standby powergenerator 104.

[0019] A starter system deactivate switch 134 monitors the speed of thestandby power generator 104 via path D, and is adapted to cause thestarter system activate switch 132 to disconnect the first capacitor 118from the starter system 108 in response to the speed of the generator104 being a predetermined minimum value for a predetermined length oftime, thus stopping the starting operation of the starter system 108.For example, if the speed of the generator 104 is determined to be 1500rpm for 5 seconds, the generator 104 is determined to be running, andthe starter system 108 is disengaged.

[0020] The transfer switch 128 is further adapted to determine a powerreturn condition of the primary power source 102, and responsivelydisconnect the standby power generator 104 from the load 106, andreconnect the primary power source 102 to the load 106. In addition, thetransfer switch 128 is adapted to shut down the standby power generator104 by disengaging the starter system enable switch 130 whichresponsively activates a shutdown system 110, which is part of thestarter system 108.

[0021] A capacitor monitor/diagnostics controller 112 is adapted viapath E to monitor the energy storage of the first capacitor 118, and toperiodically discharge and charge, i.e., exercise, the first capacitor118 to maintain a maximum desired energy storage. In addition, thecapacitor monitor/diagnostics controller 112 is adapted to generate asignal indicating the condition of the first capacitor 118, and todeliver the signal to a display monitor 114, which is described in moredetail below. In addition, the capacitor monitor/diagnostics controller112 may be adapted to perform the above functions with second, third,and fourth capacitors 120, 124, 140, although the corresponding paths tothese capacitors, i.e., corresponding to path E, are not shown in FIG.1.

[0022] In the preferred embodiment, the capacitor monitor/diagnosticscontroller 112 receives electrical power, during the transition periodbetween the primary power source 102 and the standby power generator104, from a second capacitor 120 in combination with a battery 122.Preferably, the second capacitor 120 is of the type commonly known as asuper capacitor, and provides the voltage to the capacitormonitor/diagnostics controller 112 during the transition period, and thebattery 122 provides a charging voltage to the second capacitor 120.Alternatively, the second capacitor 120 may have a capacity to providethe voltage directly without the use of a battery to charge the secondcapacitor 120. In this alternative embodiment, the battery 122 would notbe used.

[0023] A display monitor 114 is adapted to display a status condition ofat least one of the primary power source 102, the standby powergenerator 104, the starter system 108, and the first capacitor 118. Inaddition, the display monitor 114 may be adapted to display other typesof information including, but not limited to, the status of the transferswitch 128, additional operating parameters of the standby powergenerator 104, the status of other switches in the apparatus 100, andthe like.

[0024] In one embodiment, the display monitor receives informationthrough the electrical paths in the apparatus 100. For example, thestatus of the first capacitor 118 may be delivered to the displaymonitor 114 from the capacitor monitor/diagnostics controller 112 viapath F-G-H.

[0025] In another embodiment, the display monitor 114 is located at aremote location and the information is delivered by some other meansknown in the art, such as telephone lines, wireless radio, microwave,dedicated lines, and the like.

[0026] Preferably, the display monitor 114 includes an alarm 116, eitheraudio or visual or both, to notify operating personnel of statusconditions requiring attention, such as failure of the primary powersource 102, or an abnormal parameter of the standby power generator 104.

[0027] The display monitor 114 preferably receives electrical power,during the transition period between the primary power source 102 andthe standby power generator 104, from a third capacitor 124. In thepreferred embodiment, the third capacitor 124 is of the type commonlyknown as a super capacitor, and thus has the capacity to provide powerto the display monitor 114 during the transition period.

[0028] An uninterruptable power supply (UPS) 138 is electricallyconnected to the apparatus 100 and is adapted to determine a transitionbetween the primary power source 102 and the standby power supply 104via path J. During this transition period, no voltage is applied to theload 106. The UPS is adapted to responsively apply a voltage to the load106 during the transition period via path K.

[0029] In the preferred embodiment, the UPS 138 provides the voltage tothe load 106 by means of a fourth capacitor 140. Preferably, the fourthcapacitor 140 includes at least one capacitor, the number of capacitorsbeing a function of the size of the load 106. For example, for arelatively small load, one capacitor may be adequate, and a relativelylarge load may require more capacitors. The use of the fourth capacitor140 with the UPS 138 eliminates the need for batteries, thus reducingmaintenance, battery replacement costs, and the need for climatecontrol.

[0030] The first, second, third, and fourth capacitors 118, 120, 124,140 are charged by either the primary power source 102 or the standbypower generator 104 through a capacitor charge switch 136 via path I.The capacitor charge switch 136 is adapted to determine a failure of theprimary power source 102 and switch to the standby power generator 104in response. Preferably, the capacitor charge switch 136 includes an ACto DC converter 137 to provide a DC voltage to charge the first, second,third, and fourth capacitors 118, 120, 124, 140.

[0031] A system test switch 126, connected in line with the primarypower source 102 along path A, may be used to simulate failure of theprimary power source 102 for testing and diagnostics purposes.

[0032] Referring now to FIG. 2, a graph 202 of power vs. time is shown.It is noted that the scales on the axis are exemplary only, and do notindicate any values that are necessary for the present invention. Forexample, the vertical axis, i.e., power, is not assigned any units ofmeasurement, and the values given are merely arbitrary.

[0033] A representation 204 of power vs. time of the capacitor 118charging illustrates that the capacitor 118 is charged for a relativelylong period of time, for example 180 seconds, at low power. Under theseconditions, the power drain is minimized during charging of thecapacitor 118.

[0034] The power vs. time curve 206 of the first capacitor 118discharging, for example, when used to drive the starter system 108 tostart the standby power generator 104, indicates that the capacitor 118discharges a large amount of power in a short period of time. Forexample, the capacitor 118 may discharge in about 18 seconds, or aboutone tenth of the time that it took to charge the capacitor 118. Theprocess of charging the capacitor 118 at low power over a long period oftime and then discharging the capacitor 118 at high power over a shortperiod of time is known as energy compression, or pulse power. It isnoted that the 180 second charge time, the 18 second discharge time, andthe 10 to 1 energy compression ratio are merely examples used forpurposes of illustration. Other charge and discharge times and ratiosmay be used without deviating from the invention.

[0035] Referring now to FIG. 3, a graph 302 of current vs. time isshown. It is noted that the axes of the graph 302 are not drawn to anyscale and do not depict any units of measurement. The curves shown onthe graph are being used to illustrate comparative features for purposesof illustration only.

[0036] A curve 304 of the current vs. time of the capacitor 114illustrates that the capacitor 118 is capable of providing a maximumvalue of current quickly, which then slowly decreases as the capacitor118 is discharged. It is noted that the curve 304 of the capacitor 118is independent of temperature.

[0037] Curves 306, 308, 310 of the current vs. time of a battery (notshown), typically used to drive a starter system, at three temperaturesT₁, T₂, T₃ illustrate that the battery takes longer than the capacitor118 to provide maximum current for purposes of starting the standbypower generator 104. In addition, T₃ is a lower temperature than T₂,which is a lower temperature than T₁. Therefore, as shown in the graph302, as the temperature decreases, the length of time for the battery toreach maximum current output increases. This results in longer startingtimes in cold conditions, which places additional stress on the battery.In addition, the internal resistance of the battery 104 increases as thetemperature decreases. The higher internal resistance lowers the maximumoutput current of the battery 104. Therefore, as shown in FIG. 3, as thetemperature decreases, the maximum output current of the battery 104decreases.

[0038] Referring now to FIG. 4, a flow diagram illustrating a preferredmethod of the present invention is shown.

[0039] In a first decision block 402, the transfer switch 128 determinesif a power failure condition of the primary power source 102 hasoccurred. If a power failure condition has occurred, control proceeds toa first control block 404, where the transfer switch 128 transitionsfrom the primary power source 102 to the standby power generator 104.

[0040] In a second control block 406, the UPS 138 provides power to theload 106 during the transition. The UPS 138, as described above,provides power by means of at least one capacitor, i.e., the fourthcapacitor 140.

[0041] In a second decision block 408, it is determined if thetransition from the primary power source 102 to the standby power supply104 is complete; that is, if the standby power supply 104 is nowapplying power to the load 106. If the transition is complete, the powerdelivered by the UPS 138 is removed from the load 106, as depicted in athird control block 410.

[0042] In a third decision block 412, it is determined if a power returncondition of the primary power source 102 exists, i.e., if the primarypower source 102 has resumed the ability to deliver power. If the powerreturn condition exists, control proceeds to a fourth control block 414,where the transfer switch 128 provides the transition from the standbypower generator 104 to the primary power source 102.

[0043] In a fifth control block 416, the UPS 138 provides power to theload 106 during the transition. The UPS 138, as described above,provides power by means of at least one capacitor, i.e., the fourthcapacitor 140.

[0044] In a fourth decision block 418, it is determined if thetransition from the standby power generator 104 to the primary powersource 102 is complete; that is, if the primary power source 102 is nowapplying power to the load 106. If the transition is complete, the powerdelivered by the UPS 138 is removed from the load 106, as depicted in asixth control block 420.

Industrial Applicability

[0045] As an example of an application of the present invention, thefourth capacitor 140 is used to provide electrical power to the load 106of FIG. 1 during the transition periods of time between the primarypower source 102 and the standby power generator 104. The fourthcapacitor 140 is commonly known as a super capacitor; that is, thefourth capacitor 140 has a much greater capacity to store electricalenergy than typical capacitors.

[0046] Historically, batteries have been used to provide the electricalpower that is provided in the present invention by the fourth capacitor140. However, batteries require much more maintenance, have a muchshorter useful life, e.g., about three years, and do not function wellunder extreme environmental conditions, such as extreme coldtemperatures. The fourth capacitor 140 is configured and chosen to havethe storage capacity to provide the electrical power needed duringtransition periods without the inherent disadvantages of maintainingbatteries in the system.

[0047] Other aspects, objects, and features of the present invention canbe obtained from a study of the drawings, the disclosure, and theappended claims.

1. A method for providing uninterrupted power during transitions betweena primary power source and a standby power generator, including thesteps of: determining one of a power failure condition and a powerreturn condition of the primary power source; transitioning between theprimary power source and the standby power generator; and providingpower to a load during the transition, the power being supplied by anuninterruptable power supply (UPS) having a capacitor supplied voltage.2. A method, as set forth in claim 1 , wherein the capacitor suppliedvoltage is provided by at least one capacitor.
 3. A method, as set forthin claim 1 , further including the step of removing the UPS suppliedvoltage in response to determining power being supplied to the load byone of the primary power source and the standby power generator.
 4. Amethod, as set forth in claim 2 , further including the step ofmaintaining a charge on the at least one capacitor by applying a voltagefrom one of the primary power source and the standby power generator. 5.An apparatus for providing uninterrupted power during transitionsbetween a primary power source and a standby power generator comprising:a transfer switch adapted to determine one of a power failure conditionand a power return condition of the primary power source, andresponsively transition between the primary power source and the standbypower generator; an uninterruptable power supply (UPS) for providingpower to a load during the transition; and at least one capacitorelectrically connected to the UPS for providing the power to the load.6. An apparatus, as set forth in claim 5 , further including a capacitormonitor/diagnostics controller for monitoring the energy storage of theat least one capacitor, and discharging and recharging the at least onecapacitor to maintain a maximum desired energy storage.